A teenager who posted a provocative tweet based on an idea from a new film has triggered a deluge of activity on Twitter, and prompted a response from the FBI and local police.

The film, called Purge: Anarchy, depicts a fictional society in which any crime committed within an annual 12 hour window goes unpunished. The premise is that an anarchic splurge will have a calming effect on the populace for the rest of the year.

Early last week, an unidentified teenager borrowed the concept and took to Twitter calling for a real life "purge" in his home town. "Whos [sic] trying to get a Louisville Purge Started With Me?" he posted. Other students, also from the US city, began circulating the message on both Twitter and Facebook. Some included an image of a mocked-up flyer resembling the film's promotional artwork, and slated the event for the night of Friday 15 August. One tweeter even claimed to have seen the image transposed onto posters, and "hung up all over Louisville".

The messages came to the attention of the FBI and local police departments, who said they were taking the threats seriously. High school football games were reportedly cancelled. Many listened live to police radio communication - available online - and the hashtag #louisvillepolicescanner was mentioned more than 100,000 times on Twitter. "I wonder if the #LouisvillePoliceScanner operators know how famous they are tonight. This is their 'rock-star' moment," said one user.

But did the much-hyped event actually lead to a spike in recorded crime? Thankfully, the weekend passed without major incident. There were two fatal shootings on Friday night, but neither could be connected to the hoax. Dwight Mitchell, a Public Information Officer with the Louisville Metro Police Department told BBC Trending: "Luckily nothing was reported that had anything to do with a 'purge'." The police have now tracked the teenager down, and chosen not to press charges after he apologised for his tweet. "One lesson is that people really need to be careful about what they say on social media," said a spokesman for Mayor Greg Fischer.

Now, flyers have been created advertising "purges" in several other US cities as well. The Sheriff's Office of one of the cities in question has released a statement to say it is monitoring the conversation online, but does not currently see it as a legitimate threat.

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